Photoelectric conversion element and solar cell

ABSTRACT

Provided is a photoelectric conversion element including a first electrode, a hole blocking layer, an electron transport layer, a first hole transport layer, and a second electrode, wherein the first hole transport layer includes at least one of basic compounds represented by general formula (1a) and general formula (1b) below: 
     
       
         
         
             
             
         
       
         
         
           
             where in the formula (1a) or (1b), R 1  and R 2  represent a substituted or unsubstituted alkyl group or aromatic hydrocarbon group and may be identical or different, and R 1  and R 2  may bind with each other to form a substituted or unsubstituted heterocyclic group containing a nitrogen atom.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/120,464, filed on Aug. 19, 2016, which is the National Stage of theInternational Patent Application No. PCT/JP2015/052684, filed Jan. 30,2015, and claims priority to Japanese Application No. 2014-032566, filedFeb. 24, 2014 and Japanese Application No. 2014-084832, filed on Apr.16, 2014, the disclosures of all of which are incorporated herein byreference in their entireties.

TECHNICAL FIELD

The present invention relates to a method for producing a photoelectricconversion element and a solar cell.

BACKGROUND ART

In recent years, solar cells have been increasing importance asalternative energy for fossil fuels and as a measure against globalwarming. However, existing solar cells represented by silicon-basedsolar cells are expensive under the current circumstances, and theexpensiveness is a factor that prohibits popularization.

Hence, research and development for various low-cost solar cells ispromoted. Among such solar cells, dye-sensitized solar cells proposed byGraetzel et al. from Swiss Federal Institute of Technology in Lausanneare highly expected for reduction to practical use (see, e.g., Patentdocument 1 and Non-patent documents 1 and 2).

The structure of the solar cells is formed of: a porous metal oxidesemiconductor on a transparent conductive glass substrate; a dyeadsorbed to a surface of the porous metal oxide semiconductor; anelectrolyte containing a redox couple; and a counter electrode.

The dye-sensitized solar cells of Patent document 1 and Non-patentdocuments 1 and 2 are remarkably improved in photoelectric conversionefficiency by being increased in surface area using a porous material asthe electrode formed of the metal oxide semiconductor such as titaniumoxide and by having a ruthenium complex monomolecularly adsorbed as thedye.

Further, it is expected that the production costs can be reduced,because a printing technique can be applied as the method for producingthe photoelectric conversion element and no expensive productionfacilities are needed hence. However, the solar cells contain iodine anda volatile solvent and have problems that the power generatingefficiency may drop due to deterioration of the iodine redox system andthat the electrolytic solution may volatilize or leak.

As compensation for these disadvantages, the following soliddye-sensitized solar cells are proposed:

1) Solid dye-sensitized solar cells using an inorganic semiconductor(see, e.g., Non-patent documents 3 and 4);

2) Solid dye-sensitized solar cells using a low-molecular-weight organichole transport material (see, e.g., Patent document 2 and Non-patentdocuments 5 and 6); and

3) Solid dye-sensitized solar cells using a conductive polymer (see,e.g., Patent document 3 and Non-patent document 7).

The solar cell described in Non-patent document 3 uses copper iodide asa material to constitute a p-type semiconductor layer. This solar cellhas a relatively good photoelectric conversion efficiency immediatelyafter production, but it is known that the photoelectric conversionefficiency drops by half in a few hours due to deterioration attributedto, for example, increase of crystal grains of copper iodide.

Hence, the solar cell described in Non-patent document 4 additionallycontains imidazolinium thiocyanato to suppress crystallization of copperiodide. However, the suppression is not sufficient.

The solid dye-sensitized solar cell that is described in Non-patentdocument 5 and is of a type using an organic hole transport material isreported by Hagen et al. and improved by Graetzel et al. (see Non-patentdocument 6).

The solid dye-sensitized solar cell described in Patent document 2 andusing a triphenylamine compound includes a charge transport layer formedby vacuum vapor deposition of the triphenylamine compound.

Hence, the triphenylamine compound cannot reach internal voids in theporous semiconductor. Therefore, it has only been possible to obtain alow conversion efficiency.

In the example described in Non-patent document 6, a spiro-type holetransport material is dissolved in an organic solvent, and spin-coatingis employed to obtain a composite body of nano-titania particles withthe hole transport material.

In this solar cell, however, an optimum value of the thickness of anano-titania particle film is specified to be about 2 μm, which is byfar smaller than when an iodine electrolytic solution is used, i.e.,from 10 μm through 20 μm. Hence, an amount of the dye adsorbed to thetitanium oxide is low, to make it difficult to achieve sufficient lightabsorption and sufficient carrier generation. Hence, it is impossible toreach the characteristic obtained when an electrolytic solution is used.

As a solid solar cell of the type using a conductive polymer, a solidsolar cell using polypyrrole has been reported by Yanagida et al. fromOsaka University (see Non-patent document 7). This solid solar cell hasalso been able to obtain only a low conversion efficiency. A soliddye-sensitized solar cell described in Patent document 3 and using apolythiophene derivative includes a charge transfer layer formed byelectrolytic polymerization on a dye-adsorbed porous titanium oxideelectrode. However, there are problems that the dye may desorb from thetitanium oxide and that the dye may decompose. Furthermore, thepolythiophene derivative is considerably problematic in durability.

Owing to recent technological developments, driving power for electroniccircuits has been significantly reduced, and it has become possible todrive various electronic parts such as sensors by converting weak lightsuch as room light to electricity.

Further, it has been reported that existing electrolytic solution-typedye-sensitized solar cells using, for example, iodine, have aphotoelectric conversion characteristic greater than or equal toamorphous silicon solar cells under weak room light (see Non-patentdocument 8).

However, the electrolytic solution-type dye-sensitized solar cellscontain iodine and a volatile solvent described above and have problemsthat the power generating efficiency may drop due to deterioration ofthe iodine redox system and that the electrolytic solution mayvolatilize or leak.

It has also been reported that when weak light such as room light isconverted to electricity, loss current due to an internal resistance inthe photoelectric conversion element is conspicuous (see Non-patentdocument 9).

When the internal resistance is raised, a short-circuiting currentdensity worsens to degrade the photoelectric conversion characteristic.When the internal resistance is lowered, an open circuit voltage worsensto degrade the photoelectric conversion characteristic. That is, it isextremely difficult to satisfy both of; raising the internal resistance;and a good photoelectric conversion characteristic.

An open circuit voltage obtained with the photoelectric conversionelement under weak light such as the room light is lower than underpseudo sunlight. Hence, in order to obtain an output voltage needed fordriving an electronic circuit, there is a need for obtaining a high opencircuit voltage.

Hitherto, there have been reported basic substances that can achieve ahigh open circuit voltage (see Non-patent document 10). However, thereis no basic material that can achieve a photoelectric conversioncharacteristic better than hitherto used 4-tertial butylpyridine in adye-sensitized solar cell of the type using an electrolytic solutionsuch as iodine.

As described above, under the current circumstances, none of the solidphotoelectric conversion elements studied so far have been able toobtain a satisfactory characteristic.

CITATION LIST Patent Document

-   Patent document 1: Japanese Patent No. 2664194-   Patent document 2: Japanese Unexamined Patent Application    Publication No. 11-144773-   Patent document 3: Japanese Unexamined Patent Application    Publication No. 2000-106223

Non-Patent Document

-   Non-patent document 1: Nature, 353 (1991) 737-   Non-patent document 2: J. Am. Chem. Soc., 115 (1993) 6382-   Non-patent document 3: Semicond. Sci. Technol., 10 (1995) 1689-   Non-patent document 4: Electrochemistry, 70 (2002) 432-   Non-patent document 5: Synthetic Metals, 89 (1997) 215-   Non-patent document 6: Nature, 398 (1998) 583-   Non-patent document 7: Chem. Lett., (1997) 471-   Non-patent document 8: Panasonic Technical Report, 56 (2008) 87-   Non-patent document 9: Fujikura Technical Report, 121 (2011) 42-   Non-patent document 10: Solar Energy Materials & Solar Cells,    181 (2004) 87-   Non-patent document 11: J. Org. Chem, 67 (2002) 3029

SUMMARY OF INVENTION Technical Problem

The present invention has an object to solve the problems describedabove and provide a solid photoelectric conversion element having abetter photoelectric conversion characteristic than hitherto obtained.

Solution to Problem

As a result of earnest studies for solving the problems described above,it has been found possible to provide a high-performance solidphotoelectric conversion element by making a hole transport layercontain a specific basic compound. The present invention has beenarrived at on the basis of this finding.

That is, the problems are solved by a photoelectric conversion elementincluding a first electrode, a hole blocking layer, an electrontransport layer, a first hole transport layer, and a second electrode,wherein the first hole transport layer contains at least one of basiccompounds represented by a general formula (1a) and a general formula(1b) below.

In the formula (1a) or (1b), R₁ and R₂ represent a substituted orunsubstituted alkyl group or aromatic hydrocarbon group and may beidentical or different, and R₁ and R₂ may bind with each other to form asubstituted or unsubstituted heterocyclic group containing a nitrogenatom.

Effects of the Invention

The present invention can provide a solid photoelectric conversionelement having a better photoelectric conversion characteristic thanhitherto obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example schematic view illustrating a cross-section of astructure of a photoelectric conversion element of the present inventionorthogonal to a layer deposition direction.

MODE FOR CARRYING OUT THE INVENTION

A configuration of a photoelectric conversion element and a solar cellwill be described below with reference to FIG. 1.

FIG. 1 is an exemplary schematic view illustrating a cross-section ofthe photoelectric conversion element and the solar cell orthogonal to alayer deposition direction.

In the embodiment illustrated in FIG. 1, the configuration includes afirst electrode 2 on a substrate 1, a hole blocking layer 3 formed oftitanium oxide, an electron transport layer 4, a photosensitizingmaterial 5 adsorbed to the electron transport layer, and a holetransport layer 6 provided between the photosensitizing material and asecond electrode 7.

<First Electrode>

The first electrode 2 is not particularly limited so long as the firstelectrode 2 is a conductive material transparent to visible light. It ispossible to use known conductive materials used in, for example, typicalphotoelectric conversion elements or liquid crystal panels.

Examples of the material of the first electrode 2 include indium tinoxide (hereinafter referred to as ITO), fluorine-doped tin oxide(hereinafter referred to as FTO), antimony-doped tin oxide (hereinafterreferred to as ATO), indium zinc oxide, niobium titanium oxide, andgraphene. One of these materials may be deposited alone or more than oneof these materials may be laminated.

A thickness of the first electrode 2 is preferably from 5 nm through 100μm and more preferably from 50 nm through 10 μm.

It is preferable that the first electrode 2 be provided on the substrate1 formed of a material transparent to visible light, in order tomaintain a constant hardness. For example, glass, a transparent plasticplate, a transparent plastic film, or an inorganic transparentcrystalline substance is used for the substrate 1.

It is also possible to use a known integrated body of the firstelectrode 2 and the substrate 1. Examples of the integrated body includeFTO-coated glass, ITO-coated glass, zinc oxide: aluminium-coated glass,a FTO-coated transparent plastic film, and an ITO-coated transparentplastic film.

It is also possible to use a product in which a transparent electrode oftin oxide or indium oxide doped with a cation or an anion different invalence or a metal electrode formed into a light-transmissive structuresuch as a mesh form and a stripe form is provided on a substrate such asa glass substrate.

One of these materials may be used alone or two or more of thesematerials may be mixed together or laminated. Furthermore, with a viewto lowering a resistance, for example, a metal lead line may be used incombination.

Examples of the material of the metal lead line include metals such asaluminium, copper, silver, gold, platinum, and nickel. The metal leadline can be formed by a method of locating the metal lead line on thesubstrate 1 by, for example, vapor deposition, sputtering, or pressurebonding and providing the ITO or the FTO on the metal lead line.

<Hole Blocking Layer>

The hole blocking layer 3 is not particularly limited so long as thehole blocking layer is transparent to visible light and is an electrontransport material. However, titanium oxide is particularly preferable.In order to suppress loss current to achieve usability under weak lightsuch as room light, there is a need that a high internal resistance beprovided, and a film forming method of titanium oxide to form the holeblocking layer 3 is also important.

Examples of typical methods for forming a film of the titanium oxideinclude a sol-gel method and a titanium tetrachloride hydrolyzingmethod, which are wet film formation. However, a resistance obtained isslightly low. A sputtering method, which is dry film formation, is morepreferable.

The hole blocking layer 3 is formed also with a view to preventing anelectronic contact between the first electrode 2 and the hole transportlayer 6. A thickness of the hole blocking layer 3 is not particularlylimited but is preferably from 5 nm through 1 μm, more preferably from500 nm through 700 nm in wet film formation, and more preferably from 10nm through 30 nm in dry film formation.

<Electron Transport Layer>

The photoelectric conversion element and the solar cell of the presentinvention include a porous electron transport layer 4 on the holeblocking layer 3. The porous electron transport layer 4 may contain asingle layer or multiple layers.

In the case of the multiple layers, it is possible to form multiplelayers by coating dispersion liquids of semiconductor particles havingdifferent particle diameters, or it is also possible to form multiplelayers by coating different kinds of semiconductors or different resinor additive compositions.

When a sufficient thickness is not obtained with one coating, thecoating of multiple layers is an effective means.

Typically, an amount of the photosensitizing material supported by theelectron transport layer 4 per a unit projected area increases as athickness of the electron transport layer is increased, leading to anincrease in a light capture rate. However, this also increases adistance to which injected electrons diffuse, to increase loss due torecombination of charges.

Hence, the thickness of the electron transport layer 4 is preferablyfrom 100 nm through 100 μm.

The semiconductor is not particularly limited and a known semiconductormay be used.

Specific examples of the semiconductor include element semiconductorssuch as silicon and germanium, compound semiconductors represented bychalcogenides of metals, and compounds having a perovskite structure.

Examples of the chalcogenides of metals include: oxides of titanium,tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium,cerium, yttrium, lanthanum, vanadium, niobium, and tantalum; sulfides ofcadmium, zinc, lead, silver, antimony, and bismuth; selenides of cadmiumand lead; and telluride of cadmium.

Examples of other compound semiconductors include: phosphides of, forexample, zinc, gallium, indium, and cadmium; gallium arsenide;copper-indium-selenide; and copper-indium-sulfide.

Examples of the compounds having a perovskite structure includestrontium titanate, calcium titanate, sodium titanate, barium titanate,and potassium niobate. One of these semiconductors may be used alone ortwo or more of these semiconductors may be used as a mixture.

Among these semiconductors, oxide semiconductors are preferable, andtitanium oxide, zinc oxide, tin oxide, and niobium oxide areparticularly preferable. A crystal form of these semiconductors is notparticularly limited and may be monocrystalline, polycrystalline, oramorphous.

A size of the semiconductor particles is not particularly limited.However, an average primary particle diameter is preferably from 1 nmthrough 100 nm and more preferably from 5 nm through 50 nm.

It is also possible to improve efficiency based on anincident-light-scattering effect obtained by mixing or laminatingsemiconductor particles having a greater average particle diameter. Inthis case, an average particle diameter of the semiconductor particlesis preferably from 50 nm through 500 nm.

A method for producing the electron transport layer 4 is notparticularly limited. Examples of the method include a method forforming a thin film in vacuum, such as sputtering, and a wet filmforming method.

When production costs and other factors are taken into consideration,the wet film forming method is preferable, and a method of preparing apaste in which powder or sol of the semiconductor particles isdispersed, and coating an electron collecting electrode substrate withthe paste is more preferable.

In using the wet film forming method, a coating method is notparticularly limited and may be performed according to a known method.Examples of the coating method include a dipping method, a sprayingmethod, a wire bar method, a spin coating method, a roller coatingmethod, a blade coating method, and a gravure coating method. Further,as a wet printing method, various methods such as letterpress, offset,gravure, intaglio, rubber plate, and screen printing may be used.

In producing a dispersion liquid of the semiconductor particles bymechanical pulverization or using a mill, the dispersion liquid isformed by dispersing at least the semiconductor particles alone or amixture of the semiconductor particles and a resin in water or anorganic solvent.

Examples of the resin include polymers or copolymers of vinyl compoundsbased on, for example, styrene, vinyl acetate, acrylic ester, andmethacrylic ester, silicon resins, phenoxy resins, polysulfone resins,polyvinyl butyral resins, polyvinyl formal resins, polyester resins,cellulose ester resins, cellulose ether resins, urethane resins, phenolresins, epoxy resins, polycarbonate resins, polyallylate resins,polyimide resins, and polyimide resins.

Examples of the solvent in which the semiconductor particles aredispersed include water; alcohol-based solvents such as methanol,ethanol, isopropyl alcohol, and α-terpineol; ketone-based solvents suchas acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-basedsolvents such as ethyl formate, ethyl acetate, and n-butyl acetate;ether-based solvents such as diethyl ether, dimethoxyethane,tetrahydrofuran, dioxolane, and dioxane; amide-based solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, andN-methyl-2-pyrrolidone; halogenated hydrocarbon-based solvents such asdichloromethane, chloroform, bromoform, methyl iodide, dichloroethane,trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene,fluorobenzene, bromobenzene, iodobenzene, and 1-chloronaphthalene; andhydrocarbon-based solvents such as n-pentane, n-hexane, n-octane,1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene,toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, and cumene. One ofthese solvents may be used alone or two or more of these solvents may beused as a mixture solvent.

For prevention of reaggregation of particles, for example, an acid suchas hydrochloric acid, nitric acid, and acetic acid, a surfactant such aspolyoxyethylene (10) octylphenyl ether, and a chelating agent such asacetylacetone, 2-aminoethanol, and ethylene diamine may be added to thedispersion liquid of the semiconductor particles or to the paste of thesemiconductor particles obtained by, for example, a sol-gel method.

Furthermore, adding a thickener with a view to improving a film formingproperty is an effective means.

Examples of the thickener include polymers such as polyethylene glycolsand polyvinyl alcohols and thickeners such as ethyl cellulose.

It is preferable to subject the semiconductor particles after coated tofiring, microwave irradiation, electron beam irradiation, or laser lightirradiation in order to provide an electronic contact between theparticles, improve a film strength, and improve close adhesiveness withthe substrate. These treatments may be applied alone or two or morekinds of these treatments may be applied in combination.

In the firing, a firing temperature is not limited to a particularrange, but is preferably from 30° C. through 700° C. and more preferablyfrom 100° C. through 600° C. because the resistance of the substrate mayrise or the substrate may melt if the temperature is excessively high. Afiring time is also not particularly limited, but is preferably from 10minutes through 10 hours.

The microwave irradiation may be given from a side at which the electrontransport layer 4 is formed or from a back side.

An irradiation time is not particularly limited, but is preferablywithin 1 hour.

After firing, chemical plating using an aqueous solution of titaniumtetrachloride or a mixture solution of titanium tetrachloride with anorganic solvent or an electrochemical plating treatment using a titaniumtrichloride aqueous solution may be performed with a view to increasinga surface area of the semiconductor particles and increasing efficiencyof electron injection from the photosensitizing material into thesemiconductor particles.

A porous state is formed in the film obtained by depositing thesemiconductor particles having a diameter of several tens of nanometersby, for example, sintering. This nanoporous structure has an extremelylarge surface area. The surface area can be expressed by a roughnessfactor.

The roughness factor is a value representing an actual area inside theporous texture relative to an area of the semiconductor particles coatedon the substrate. Hence, a greater roughness factor is more preferable.However, considering the relationship with the film thickness of theelectron transport layer 4, the roughness factor is preferably 20 orgreater in the present invention.

<Photosensitizing Material>

In the present invention, in order to further improve the conversionefficiency, a photosensitizing material is adsorbed to a surface of theelectron transport semiconductor, which is the electron transport layer4. A substance represented by a general formula (2) is preferable as thephotosensitizing material.

In the formula, R₃ represents a substituted or unsubstituted alkylgroup.

Specific exemplary compounds of the general formula (2) will bepresented below. However, these compounds are non-limiting examples.

Dye 1 R₃═CH₂CH₃ (Japan Chemical Substance Dictionary Nos. J2.477.478Cand J3.081.465G) Dye 2 R₃═(CH₂)₃CH₃ Dye 3 R₃═C(CH₃)₃ Dye 4 R₃═(CH₂)₉CH₃Dye 5 R₃═(CH₂)₂COOH Dye 6 R₃═(CH₂)₄COOH Dye 7 R₃═(CH₂)₇COOH Dye 8R₃═(CH₂)₁₀COOH (Japan Chemical Substance Dictionary No. J3.113.583D)

A compound represented by the general formula (2) can be synthesized bya method described in Dye and Pigments 91 (2011) pp. 145-152.

The photosensitizing material 5 is not limited to the compoundspresented above so long as the photosensitizing material is a compoundoptically excitable by excitation light used. Specific examples of thephotosensitizing material also include the following.

Specific examples of the photosensitizing material include: metalcomplex compounds described in, e.g., Japanese Translation of PCTInternational Application Publication No. JP-T-07-500630, JapaneseUnexamined Patent Application Publication Nos. 10-233238, 2000-26487,2000-323191, and 2001-59062; coumarin compounds described in, e.g.,Japanese Unexamined Patent Application Publication Nos. 10-93118,2002-164089 and 2004-95450, and J. Phys. Chem. C, 7224, Vol. 111 (2007);polyene compounds described in, e.g., Japanese Unexamined PatentApplication Publication No. 2004-95450 and Chem. Commun., 4887 (2007);indoline compounds described in, e.g., Japanese Unexamined PatentApplication Publication Nos. 2003-264010, 2004-63274, 2004-115636,2004-200068, and 2004-235052, J. Am. Chem. Soc., 12218, Vol. 126 (2004),Chem. Commun., 3036 (2003), and Angew. Chem. Int. Ed., 1923, Vol. 47(2008); thiophene compounds described in, e.g., J. Am. Chem. Soc.,16701, Vol. 128 (2006) and J. Am. Chem. Soc., 14256, Vol. 128 (2006);cyanine dyes described in, e.g., Japanese Unexamined Patent ApplicationPublication Nos. 11-86916, 11-214730, 2000-106224, 2001-76773, and2003-7359; merocyanine dyes described in, e.g., Japanese UnexaminedPatent Application Publication Nos. 11-214731, 11-238905, 2001-52766,2001-76775, and 2003-7360; 9-arylxanthene compounds described in, e.g.,Japanese Unexamined Patent Application Publication Nos. 10-92477,11-273754, 11-273755, and 2003-31273; triarylmethane compounds describedin, e.g., Japanese Unexamined Patent Application Publication Nos.10-93118 and 2003-31273; and phthalocyanine compounds and porphyrincompounds described in, e.g., Japanese Unexamined Patent ApplicationPublication Nos. 09-199744, 10-233238, 11-204821 and 11-265738, J. Phys.Chem., 2342, Vol. 91 (1987), J. Phys. Chem. B, 6272, Vol. 97 (1993),Electroanal. Chem., 31, Vol. 537 (2002), Japanese Unexamined PatentApplication Publication No. 2006-032260, J. Porphyrins Phthalocyanines,230, Vol. 3 (1999), Angew. Chem. Int. Ed., 373, Vol. 46 (2007), andLangmuir, 5436, Vol. 24 (2008).

Among these photosensitizing materials, the metal complex compounds, thecoumarin compounds, the polyene compounds, the indoline compounds, andthe thiophene compounds are preferable.

As a method for adsorbing the photosensitizing material 5 to theelectron transport layer 4, it is possible to use a method of immersingthe electron collecting electrode containing the semiconductor particlesin a photosensitizing material solution or dispersion liquid and amethod of coating the electron transport layer with the solution or thedispersion liquid to adsorb the photosensitizing material.

As the method of immersing the electron collecting electrode containingthe semiconductor particles in the photosensitizing material solution ordispersion liquid, for example, an immersing method, a dipping method, aroller method, and an air knife method may be used.

As the method of coating the electron transport layer with the solutionor the dispersion liquid to adsorb the photosensitizing material, forexample, a wire bar method, a slide hopper method, an extrusion method,a curtain method, a spinning method, and a spraying method may be used.

The photosensitizing material may be adsorbed under a supercriticalfluid using, for example, carbon dioxide.

In adsorbing the photosensitizing material 5, a condensing agent may beused in combination.

The condensing agent may be any of: a substance that is assumed tocatalyze physical or chemical binding of the photosensitizing materialand the electron transport compound with a surface of an inorganicsubstance; and a substance that acts stoichiometrically to cause achemical equilibrium to move in an advantageous manner.

Furthermore, thiol or a hydroxy compound may be added as the condensingaid.

Examples of a solvent in which the photosensitizing material 5 isdissolved or dispersed include: water; alcohol-based solvents such asmethanol, ethanol, and isopropyl alcohol; ketone-based solvents such asacetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-basedsolvents such as ethyl formate, ethyl acetate, and n-butyl acetate;ether-based solvents such as diethyl ether, dimethoxyethane,tetrahydrofuran, dioxolane, and dioxane; amide-based solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, andN-methyl-2-pyrrolidone; halogenated hydrocarbon-based solvents such asdichloromethane, chloroform, bromoform, methyl iodide, dichloroethane,trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene,fluorobenzene, bromobenzene, iodobenzene, and 1-chloronaphthalene; andhydrocarbon-based solvents such as n-pentane, n-hexane, n-octane,1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene,toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, and cumene. One ofthese solvents may be used alone or two or more of these solvents may beused as a mixture.

Some kinds of the photosensitizing materials act more effectively whenaggregation between different compounds is suppressed. Hence, adeaggregating agent may be used in combination.

As the deaggregating agent, steroid compounds such as cholic acid andchenodeoxycholic acid, long-chain alkylcarboxylic acids, or long-chainalkylphosphonic acids are preferable. An appropriate deaggregating agentis selected depending on the dye used.

An amount of the deaggregating agent added is preferably from 0.01 partsby mass through 500 parts by mass and more preferably from 0.1 parts bymass through 100 parts by mass relative to 1 part by mass of the dye.

A temperature in adsorbing the photosensitizing material alone or atemperature in adsorbing the photosensitizing material together with thedeaggregating agent is preferably −50° C. or higher but 200° C. orlower.

The adsorption may be performed in a still state or under stirring.

A method for the stirring is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe method include a stirrer, a ball mill, a paint conditioner, a sandmill, an attritor, a disperser, and ultrasonic dispersion.

A time needed for the adsorption is preferably 5 seconds or longer but1,000 hours or shorter, more preferably 10 seconds or longer but 500hours or shorter, and yet more preferably 1 minute or longer but 150hours or shorter.

Furthermore, it is preferable to perform the adsorption in a dark place.

<Hole Transport Layer>

The hole transport material 6 is not particularly limited and may beappropriately selected depending on the intended purpose so long as thehole transport material contains an organic hole transport material andat least one of basic compounds represented by a general formula (1a)and a general formula (1b).

As a typical hole transport layer, for example, an electrolytic solutionobtained by dissolving a redox couple in an organic solvent, a gelelectrolyte obtained by immersing in a polymer matrix, a liquid obtainedby dissolving a redox couple in an organic solvent, a molten saltcontaining a redox couple, a solid electrolyte, an inorganic holetransport material, and an organic hole transport material are used.

<<Organic Hole Transport Material>>

The organic hole transport material can be used in both of a holetransport layer 6 having a single-layer structure formed of a singlematerial and a hole transport layer 6 having a laminated structureformed of a plurality of compounds.

A known organic hole transport compound is used as the organic holetransport material used in the single-layer structure formed of a singlematerial.

Specific examples of the known organic hole transport compound include:oxadiazole compounds presented in, e.g., Japanese Examined PatentPublication No. 34-5466; triphenylmethane compounds presented in, e.g.,Japanese Examined Patent Publication No. 45-555; pyrazoline compoundspresented in, e.g., Japanese Examined Patent Publication No. 52-4188;hydrazone compounds presented in, e.g., Japanese Examined PatentPublication No. 55-42380; oxadiazole compounds presented in, e.g.,Japanese Unexamined Patent Application Publication No. 56-123544;tetraarylbenzidine compounds presented in Japanese Unexamined PatentApplication Publication No. 54-58445; stilbene compounds presented inJapanese Unexamined Patent Application Publication No. 58-65440 orJapanese Unexamined Patent Application Publication No. 60-98437; andspirobifluorene-based compounds such as spiro-OMeTAD described in Adv,Mater., 813, vol. 17, (2005),

Among these organic hole transport compounds, the hole transportmaterial called spiro-OMeTAD mentioned above is preferable because thishole transport material exhibits an excellent photoelectric conversioncharacteristic.

A known hole transportable polymer material is used as the polymermaterial to be used near the second electrode 7 in the hole transportlayer 6 used in the form of the laminated structure.

Specific examples of the known hole transportable polymer materialinclude:

polythiophene compounds such as poly(3-n-hexylthiophene),poly(3-n-octyloxythiophene), poly(9,9′-dioctyl-fluorene-co-bithiophene),poly(3,3′″-didodecyl-quarter thiophene),poly(3,6-dioctylthieno[3,2-b]thiophene),poly(2,5-bis(3-decylthiophen-2-yl)thieno[3,2-b]thiophene),poly(3,4-didecylthiophene-co-thieno[3,2-b]thiophene),poly(3,6-dioctylthieno[3,2-b]thiophene-co-thieno[3,2-b]thiophene),poly(3,6-dioctylthieno[3,2-b]thiophene-co-thiophene), andpoly(3,6-dioctylthieno[3,2-b]thiophene-co-bithiophene);

polyphenylenevinylene compounds such aspoly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene],poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene], andpoly[(2-methoxy-5-(2-ethylphexyloxy)-1,4-phenylenevinylene)-co-(4,4′-biphenylene-vinylene)];

polyfluorene compounds such as poly(9,9′-didodecylfluorenyl-2,7-diyl),poly[(9,9-dioctyl-2,7-divinylenefluorene)-alt-co-(9,10-anthracene)],poly[(9,9-dioctyl-2,7-divinylenefluorene)-alt-co-(4,4′-biphenylene)],poly[(9,9-dioctyl-2,7-divinylenefluorene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)],and poly[(9,9-dioctyl-2,7-diyl)-co-(1,4-(2,5-dihexyloxy)benzene)];

polyphenylene compounds such as poly[2,5-dioctyloxy-1,4-phenylene] andpoly[2,5-di(2-ethylhexyloxy-1,4-phenylene];

polyarylamine compounds such aspoly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(N,N′-diphenyl)-N,N′-di(p-hexylphenyl)-1,4-diaminobenzene],poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(N,N′-bis(4-octyloxyphenyl)benzidine-N,N′-(1,4-diphenylene)],poly[(N,N′-bis(4-octyloxyphenyl)benzidine-N,N′-(1,4-diphenylene)],poly[N,N′-bis(4-(2-ethylhexyloxy)phenyl)benzidine-N,N′-(1,4-diphenylene)],poly[phenylimino-1,4-phenylenevinylene-2,5-dioctyloxy-1,4-phenylenevinylene-1,4-phenylene],poly[p-tolylimino-1,4-phenylenevinylene-2,5-di(2-ethylhexyloxy)-1,4-phenylenevinylene-1,4-phenylene],and poly[4-(2-ethylhexyloxy)phenylimino-1,4-biphenylene]; and

polythiadiazole compounds such aspoly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo(2,1′,3)thiadiazole]and poly(3,4-didecylthiophene-co-(1,4-benzo(2,1′,3)thiadiazole).

Among these hole transportable polymer materials, the polythiophenecompounds and the polyarylamine compounds are particularly preferable,considering carrier mobility and ionization potential.

Various additives may be added in the organic hole transport material.

Examples of the additives include: iodine; metal iodides such as lithiumiodide, sodium iodide, potassium iodide, cesium iodide, calcium iodide,copper iodide, iron iodide, and silver iodide; quaternary ammonium saltssuch as tetraalkylammonium iodide and pyridinium iodide; metal bromidessuch as lithium bromide, sodium bromide, potassium bromide, cesiumbromide, and calcium bromide; bromine salts of quaternary ammoniumcompounds, such as tetraalkylammonium bromide and pyridinium bromide;metal chlorides such as copper chloride and silver chloride; metalacetates such as copper acetate, silver acetate, and palladium acetate;metal sulfates such as copper sulfate and zinc sulfate; metal complexessuch as ferrocyanate-ferricyanate and ferrocene-ferricinium ion; sulfurcompounds such as polysodium sulfide and alkylthiol-alkyldisulfide;viologen dyes, hydroquinone, etc.; ionic liquids described in Inorg.Chem. 35 (1996) 1168, such as 1,2-dimethyl-3-n-propylimidazoliniumiodide, 1-methyl-3-n-hexylimidazolinium iodide,1,2-dimethyl-3-ethylimidazoliumtrifluoromethane sulfonic acid salt,1-methyl-3-butylimidazoliumnonafluorobutyl sulfonic acid salt, and1-methyl-3-ethylimidazoliumbis(trifluoromethyl)sulfonylimide; basiccompounds such as pyridine, 4-t-butylpyridine, and benzimidazole; andlithium compounds such as lithium trifluoromethane sulfonylimide andlithium diisopropylimide.

<<Basic Compounds>>

In the present invention, by addition of a basic compound represented bya general formula (1a) or a general formula (1b) below in the organichole transport material, a particularly high open circuit voltage can beobtained.

Furthermore, an internal resistance in the photoelectric conversionelement rises to enable reduction of loss current under weak light suchas room light. Hence, it is possible to obtain an open circuit voltagehigher than obtained with an existing basic compound.

In the formula (1a) or (1b), R₁ and R₂ represent a substituted orunsubstituted alkyl group or aromatic hydrocarbon group and may beidentical or different, and R₁ and R₂ may bind with each other to form asubstituted or unsubstituted heterocyclic group containing a nitrogenatom. Examples of the substituent include alkyl groups, aromatichydrocarbon groups, and substituted or unsubstituted alkoxy groups.

Hitherto, there have been known compounds that have a similar structureto the general formula (1a) or the general formula (1b) and areclassified into the basic compounds presented below. Some of thesecompounds are known to have been used as basic compounds in iodineelectrolytic solution-type dye-sensitized solar cells. These compoundsprovide a high open circuit voltage, but have been reported tosignificantly reduce a short-circuiting current density and considerablyworsen a photoelectric conversion characteristic.

The hole transport layer 6 uses the organic hole transport materialdescribed above and is different from a hole transport model based on,for example, the iodine electrolytic solution.

Hence, reduction of a short-circuiting current density is low and a highopen circuit voltage can be obtained, to make it possible to obtain anexcellent photoelectric conversion characteristic. Furthermore, it couldbe verified that a particularly outstanding excellent performance wasexhibited in photoelectric conversion under weak light such as roomlight. This photoelectric conversion is a scarcely reported case.

Specific exemplary compounds of the general formula (1a) or the generalformula (1b) are presented in Table 1 (Table 1-1 and Table 1-2) below.However, these compounds are non-limiting examples.

TABLE 1

Compound No. 1

Compound No. 2

Compound No. 3

Compound No. 4

Compound No. 5

Compound No. 6

Compound No. 7

Compound No. 8

Compound No. 9

Compound No. 10

Compound No. 11

Compound No. 12

Compound No. 13

Compound No. 14

Compound No. 15

Compound No. 16

Compound No. 17

Compound No. 18

Compound No. 19

Compound No. 20

Compound No. 21

Compound No. 22

Compound No. 23

Compound No. 24

Compound No. 25

Compound No. 26

Compound No. 27

Compound No. 28

Compound No. 29

Compound No. 30

Compound No. 31

An amount of the basic compound represented by the general formula (1a)or the general formula (1b) added in the hole transport layer 6 ispreferably 1 part by mass or greater but 20 parts by mass or less andmore preferably 5 parts by mass or greater but 15 parts by mass or lessrelative to 100 parts by mass of the organic hole transport material.

<Method for Synthesizing the Basic Material (1a) or (1b) Used in thePresent Invention>

The basic material can be easily synthesized through the route presentedbelow, in the same manner as in a reported case (J. Org. Chem., 67(2002) 3029).

In the formulae (a) and (b), R₁ and R₂ represent a substituted orunsubstituted alkyl group or aromatic hydrocarbon group and may beidentical or different. R₁ and R₂ may bind with each other to form asubstituted or unsubstituted heterocyclic group containing a nitrogenatom. X represents a halogen.

With a view to improving conductivity, an oxidizing agent for changingpart of the organic hole transport material to a radical cation may beadded.

Examples of the oxidizing agent include tris(4-bromophenyl)aminiumhexachloroantimonate, silver hexafluoroantimonate, nitrosoniumtetrafluoroborate, silver nitrate, and cobalt complex-based compounds.

There is no need that the whole of the organic hole transport materialbe oxidized by addition of the oxidizing agent. Only part of the organichole transport material needs to be oxidized. It is optional whether theadded oxidizing agent is removed or not to the outside of the systemafter addition.

The hole transport layer 6 is formed directly on the electron transportlayer 4 supporting the photosensitizing material. A method for producingthe hole transport layer 6 is not particularly limited. Examples of themethod include a method for forming a thin film in vacuum, such asvacuum vapor deposition, and a wet film forming method. Consideringproduction costs and other factors, the wet film forming method isparticularly preferable, and a method for coating the electron transportlayer 4 with the hole transport layer is preferable.

In using the wet film forming method, a coating method is notparticularly limited and may be performed according to a known method.Examples of the coating method include a dipping method, a sprayingmethod, a wire bar method, a spin coating method, a roller coatingmethod, a blade coating method, and a gravure coating method. Further,as a wet printing method, various methods such as letterpress, offset,gravure, intaglio, rubber plate, and screen printing may be used.

Film formation may be performed under a supercritical fluid or asubcritical fluid having a temperature/pressure lower than a criticalpoint.

The supercritical fluid is not particularly limited and may beappropriately selected depending on the intended purpose so long as thesupercritical fluid exists as a non-condensable high-density fluid intemperature and pressure ranges higher than a limit (critical point)until which a gas and a liquid can coexist, and even when compressed,does not condense but is maintained at higher than or equal to acritical temperature and higher than or equal to a critical pressure.However, a supercritical fluid having a low critical temperature ispreferable.

Preferable examples of the supercritical fluid include carbon monoxide,carbon dioxide, ammonia, nitrogen, water, alcohol-based solvents such asmethanol, ethanol, and n-butanol, hydrocarbon-based solvents such asethane, propane, 2,3-dimethylbutane, benzene, and toluene, halogen-basedsolvents such as methylene chloride and chlorotrifluoromethane, andether-based solvents such as dimethyl ether. Among these supercriticalfluids, the carbon dioxide is particularly preferable because the carbondioxide has a critical pressure of 7.3 MPa and a critical temperature of31° C., and hence can form a supercritical state easily and isincombustible and easy to handle.

One of these fluids may be used alone or two or more of these fluids maybe used as a mixture.

The subcritical fluid is not particularly limited and may beappropriately selected depending on the intended purpose so long as thesubcritical fluid exists as a high-pressure liquid in temperature andpressure ranges near critical points.

The compounds raised as examples of the supercritical fluid can also beused favorably as the subcritical fluid.

A critical temperature and a critical pressure of the supercriticalfluid are not particularly limited and may be appropriately selecteddepending on the intended purpose. However, the critical temperature ispreferably −273° C. or higher but 300° C. or lower and particularlypreferably 0° C. or higher but 200° C. or lower.

In addition to the supercritical fluid and the subcritical fluid, anorganic solvent and an entrainer may further be used in combination.

Addition of the organic solvent and the entrainer makes it easier toadjust solubility to the supercritical fluid.

The organic solvent is not particularly limited and may be appropriatelyselected depending on the intended purpose. Examples of the organicsolvent include: ketone-based solvents such as acetone, methyl ethylketone, and methyl isobutyl ketone; ester-based solvents such as ethylformate, ethyl acetate, and n-butyl acetate; ether-based solvents suchas diisopropyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, anddioxane; amide-based solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; halogenatedhydrocarbon-based solvents dichloromethane, chloroform, bromoform,methyl iodide, dichloroethane, trichloroethane, trichloroethylene,chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene,iodobenzene, and 1-chloronaphthalene; and hydrocarbon-based solventssuch as n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane,methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m-xylene,p-xylene, ethylbenzene, and cumene.

A press process step may be provided after the organic hole transportmaterial is provided on the first electrode 2 provided with the electrontransport material coated with the photosensitizing material.

It is considered that the press process makes close adhesion of theorganic hole transport material with the porous electrode stronger toimprove efficiency.

A method for the press process is not particularly limited. Examples ofthe method include a press forming method using a flat plate representedby an IR tablet molding machine, and a roll press method using, forexample, a roller.

A pressure in the press process is preferably 10 kgf/cm² or higher andmore preferably 30 kgf/cm² or higher. A time for which the press processis performed is not particularly limited but is preferably within 1hour.

Heat may be applied during the press process.

In the press process, a release material may be interposed between apress machine and the electrode.

Examples of the release material include fluororesins such aspolytetrafluoroethylene, polychlorotrifluoroethylene,tetrafluoroethylene-hexafluoropropylene copolymers, perfluoroalkoxyfluoride resins, polyvinylidene fluoride, ethylene-tetrafluoroethylenecopolymers, ethylene-chlorotrifluoroethylene copolymers, and polyvinylfluoride.

After the press process step, a metal oxide may be provided between theorganic hole transport material and the second electrode 7, before thecounter electrode is provided. Examples of the metal oxide includemolybdenum oxide, tungsten oxide, vanadium oxide, and nickel oxide.Among these metal oxides, the molybdenum oxide is particularlypreferable.

As described above, the hole transport layer 6 may have a single-layerstructure formed of a single material or a laminated structure formed ofa plurality of compounds. In the case of the laminated structure, it ispreferable to use a polymer material in the organic hole transportmaterial layer near the second electrode 7.

This is because use of the polymer material having an excellent filmforming property can make the surface of the porous electron transportlayer 4 smoother and can improve the photoelectric conversioncharacteristic.

Furthermore, it is difficult for the polymer material to permeate theinside of the porous electron transport layer 4. This conversely makesthe polymer material excellent in coating the surface of the porouselectron transport layer 4 and effective for preventing short circuitingwhen an electrode is provided, leading to a higher performance.

<Second Electrode>

A method for providing the metal oxide on the organic hole transportmaterial is not particularly limited. Examples of the method include amethod for forming a thin film in vacuum, such as sputtering and vacuumvapor deposition, and a wet film forming method.

As the wet film forming method, preferable is a method of preparing apaste obtained by dispersing powder or sol of the metal oxide, andcoating the hole transport layer 6 with the paste.

In using the wet film forming method, a coating method is notparticularly limited and may be performed according to a known method.Examples of the coating method include a dipping method, a sprayingmethod, a wire bar method, a spin coating method, a roller coatingmethod, a blade coating method, and a gravure coating method. Further,as a wet printing method, various methods such as letterpress, offset,gravure, intaglio, rubber plate, and screen printing may be used. Athickness of the second electrode is preferably from 0.1 nm through 50nm and more preferably from 1 nm through 10 nm.

The second electrode 7 is newly provided after the hole transport layer6 is formed or newly provided on the metal oxide.

Typically, the same configuration as the first electrode 2 describedabove can be used as the second electrode 7. A support is notindispensable for a configuration of which strength and seal can besufficiently maintained.

Examples of the material of the second electrode 7 include: metals suchas platinum, gold, silver, copper, and aluminium; carbon-based compoundssuch as graphite, fullerene, carbon nanotube, and graphene; conductivemetal oxides such as ITO, FTO, and ATO; and conductive polymers such aspolythiophene and polyaniline.

The thickness of the second electrode 7 is not particularly limited.Hence, the materials for the second electrode 7 may be used alone, ortwo or more of the materials may be used as a mixture.

Formation of the second electrode 7 by coating can be performed byappropriate methods such as coating, lamination, vapor deposition, CVD,and pasting on the hole transport layer 6, depending on the kind of thematerial used and the kind of the hole transport layer C.

In order to enable operation as a dye-sensitized solar cell, at leastone of the first electrode 2 and the second electrode 7 needs to besubstantially transparent.

In the dye-sensitized solar cell of the present invention, the firstelectrode 2 is transparent. A preferable manner is that sunlight is madeincident from the first electrode 2 side. In this case, it is preferableto use a light-reflecting material at the second electrode 7 side.Metals, glass on which a conductive oxide is vapor-deposited, plastics,and metallic thin films are preferable.

Further, providing an antireflection layer at a sunlight incident sideis an effective means.

<Applications>

The dye-sensitized solar cell of the present invention can be applied topower supply devices using a solar cell.

Application examples include all devices that hitherto have utilized asolar cell or a power supply device using a solar cell.

Needless to say, the dye-sensitized solar cell may be used as, forexample, a solar cell for a desk-top electronic calculator or awristwatch. However, a power supply device to be mounted on, forexample, a portable phone, an electronic organizer, and an electronicpaper can be raised as examples that take advantage of thecharacteristic of the photoelectric conversion element of the presentinvention. Furthermore, an auxiliary power supply intended for extendinga continuously usable time of rechargeable or dry cell-operated electricappliances can be raised as an application example.

EXAMPLES

The present invention will be specifically described below by way ofExamples. However, embodiments of the present invention should not beconstrued as being limited to the Examples.

Example 1

(Production of Titanium Oxide Semiconductor Electrode)

Titanium tetra-n-propoxide (2 ml), acetic acid (4 ml), ion-exchangedwater (1 ml), and 2-propanol (40 ml) were mixed, spin-coated on a FTOglass substrate, dried at room temperature, and fired in air at 450° C.for 30 minutes, to produce a titanium oxide semiconductor electrode.

The same solution was again spin-coated on the obtained electrode to afilm thickness of 100 nm and fired in air at 450° C. for 30 minutes, toform a hole blocking layer.

Titanium oxide (available from Nippon Aerosil Co., Ltd., P90) (3 g),acetylacetone (0.2 g), and a surfactant (available from Wako PureChemical Industries, Ltd., polyoxyethylene octylphenyl ether: TRITONX-100) (0.3 g) were subjected to a bead mill treatment for 12 hourstogether with water (5.5 g) and ethanol (1.0 g).

Polyethylene glycol (#20,000) (1.2 g) was added to the obtaineddispersion liquid, to produce a paste.

The paste was coated on the hole blocking layer to a thickness of 1.5μm, dried at room temperature, and fired in air at 500° C. for 30minutes, to form a porous electron transport layer.

(Production of Dye-Sensitized Solar Cell)

The titanium oxide semiconductor electrode described above was immersedin a sensitizing dye, which was the Dye 8 mentioned above (0.5 mM, anacetonitrile/t-butanol (volume ratio of 1:1) solution), and left tostand still in a dark place for 1 hour, to adsorb the photosensitizingmaterial.

The semiconductor electrode supporting the photosensitizing agent wasspin-coated with a solution obtained by adding lithiumbis(trifluoromethanesulfonyl)imide (with a solid content of 1% by mass)available from Kanto Chemical Co., Inc. and the exemplary basic compoundNo. 1 (with a solid content of 1.4% by mass) to a solution of an organichole transport material (available from Merck Ltd., product name:2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene,product number: SHT-263) dissolved in chlorobenzene (with a solidcontent of 14% by mass), to form a hole transport layer. Silver wasvacuum-vapor deposited on the hole transport layer to a thickness of 100nm, to produce a dye-sensitized solar cell.

(Evaluation of Dye-Sensitized Solar Cell)

A photoelectric conversion efficiency of the obtained dye-sensitizedsolar cell under white LED irradiation (0.05 mW/cm²) was measured. Themeasurement was performed using a desk lamp CDS-90α (study mode)available from Cosmotechno. Co., Ltd. as the white LED, and a solar cellevaluation system, AS-510-PV03 available from NF Corporation as anevaluator. As a result, excellent characteristics were exhibited,including an open circuit voltage of 0.82 V, a short-circuiting currentdensity of 8.20 μA/cm², a form factor of 0.78, and a conversionefficiency of 10.48%.

Example 2

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 3, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 3

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 5, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 4

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 8, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 5

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 10, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 6

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 12, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 7

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 1,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 13, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 8

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 1,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 15, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 9

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 1,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 16, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 10

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 4,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 18, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 11

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 4,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 20, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 12

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 4,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 13, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 13

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 8,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 13, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 14

A dye-sensitized solar cell was produced in the same manner as inExample 1, except that lithium bis(trifluoromethanesulfonyl)imide ofExample 1 was changed to 1-n-hexyl-3-methylimidazoliniumbis(trifluoromethylsulfonyl)imide, and was evaluated. The results arepresented in Table 2 and Table 3.

Example 15

A dye-sensitized solar cell was produced in the same manner as inExample 1, except that a hole transport layer described below wasinserted between the hole transport layer and silver electrode ofExample 1, and was evaluated. The results are presented in Table 2 andTable 3.

The hole transport layer was spray-coated with a solution obtained byadding 1-n-hexyl-3-methylimidazolinium trifluorosulfonyldiimide (27 mM)to chlorobenzene in which poly(3-n-hexylthiophene) available fromSigma-Aldrich Corporation had been dissolved (with a solid content of 2%by mass), to form a film of about 100 nm.

Example 16

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 8,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 21, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 17

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 23, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 18

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 24, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 19

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 26, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 20

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 28, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 21

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed tothe basic compound represented by the exemplary compound No. 29, and wasevaluated. The results are presented in Table 2 and Table 3.

Example 22

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 1,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 26, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 23

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 1,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 30, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 24

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 1,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 31, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 25

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 4,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 21, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 26

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 4,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 26, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 27

A photoelectric conversion element was produced in the same manner as inExample 1, except that the dye of Example 1 was changed to a dye, Dye 4,and the basic compound of Example 1 was changed to the basic compoundrepresented by the exemplary compound No. 28, and was evaluated. Theresults are presented in Table 2 and Table 3.

Example 28

A dye-sensitized solar cell was produced in the same manner as inExample 1, except that lithium bis(trifluoromethanesulfonyl)imide ofExample 1 was changed to 1-n-hexyl-3-methylimidazoliniumbis(trifluoromethylsulfonyl)imide, and was evaluated. The results arepresented in Table 2 and Table 3.

Example 29

A dye-sensitized solar cell was produced in the same manner as inExample 16, except that a hole transport layer described below wasinserted between the hole transport layer and silver electrode ofExample 16, and was evaluated. The results are presented in Table 2 andTable 3.

The hole transport layer was spray-coated with a solution obtained byadding 1-n-hexyl-3-methylimidazolinium trifluorosulfonyldiimide (27 mM)to chlorobenzene in which poly(3-n-hexylthiophene) available fromSigma-Aldrich Corporation was dissolved (with a solid content of 2% bymass), to form a film of about 100 nm.

Comparative Example 1

A photoelectric conversion element was produced in the same manner as inExample 1, except that the basic compound of Example 1 was changed totertial butylpyridine available from Sigma-Aldrich Corporation, and wasevaluated. The results are presented in Table 2 and Table 3.

TABLE 2 Materials added to solution in which organic hole transportmaterial was dissolved Example Basic No. Dye compound ElectrolyteRemarks 1 8 No. 1 Lithium bis(trifluoromethanesulfonyl)imide 2 8 No. 3Lithium bis(trifluoromethanesulfonyl)imide 3 8 No. 5 Lithiumbis(trifluoromethanesulfonyl)imide 4 8 No. 8 Lithiumbis(trifluoromethanesulfonyl)imide 5 8 No. 10 Lithiumbis(trifluoromethanesulfonyl)imide 6 8 No. 12 Lithiumbis(trifluoromethanesulfonyl)imide 7 1 No. 13 Lithiumbis(trifluoromethanesulfonyl)imide 8 1 No. 15 Lithiumbis(trifluoromethanesulfonyl)imide 9 1 No. 16 Lithiumbis(trifluoromethanesulfonyl)imide 10 4 No. 18 Lithiumbis(trifluoromethanesulfonyl)imide 11 4 No. 20 Lithiumbis(trifluoromethanesulfonyl)imide 12 4 No. 13 Lithiumbis(trifluoromethanesulfonyl)imide 13 8 No. 13 Lithiumbis(trifluoromethanesulfonyl)imide 14 8 No. 11-n-hexyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)imide 15 8No. 1 Lithium bis(trifluoromethanesulfonyl)imide Another hole transportlayer was inserted between hole transport layer and silver electrode 168 No. 21 Lithium bis(trifluoromethanesulfonyl)imide 17 8 No. 23 Lithiumbis(trifluoromethanesulfonyl)imide 18 8 No. 24 Lithiumbis(trifluoromethanesulfonyl)imide 19 8 No. 26 Lithiumbis(trifluoromethanesulfonyl)imide 20 8 No. 28 Lithiumbis(trifluoromethanesulfonyl)imide 21 8 No. 29 Lithiumbis(trifluoromethanesulfonyl)imide 22 1 No. 26 Lithiumbis(trifluoromethanesulfonyl)imide 23 1 No. 30 Lithiumbis(trifluoromethanesulfonyl)imide 24 1 No. 31 Lithiumbis(trifluoromethanesulfonyl)imide 25 4 No. 21 Lithiumbis(trifluoromethanesulfonyl)imide 26 4 No. 26 Lithiumbis(trifluoromethanesulfonyl)imide 27 4 No. 28 Lithiumbis(trifluoromethanesulfonyl)imide 28 8 No. 211-n-hexyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)imide 29 8No. 21 Lithium bis(trifluoromethanesulfonyl)imide Another hole transportlayer was inserted between hole transport layer and silver electrodeComparative 8 Tertial Lithium bis(trifluoromethanesulfonyl)imide Example1 butyl pyridine

TABLE 3 Open circuit Short-circuiting Conversion Example voltage currentdensity Form efficiency No. (V) (μA/cm²) factor (%) 1 0.82 8.20 0.7810.48 2 0.83 7.95 0.76 10.02 3 0.83 8.04 0.75 10.00 4 0.81 8.32 0.7610.24 5 0.75 8.52 0.79 10.09 6 0.81 8.45 0.78 10.67 7 0.85 8.28 0.7810.97 8 0.87 7.85 0.76 10.38 9 0.80 8.25 0.79 10.42 10 0.82 8.25 0.7810.55 11 0.78 8.31 0.79 10.24 12 0.84 8.25 0.77 10.67 13 0.86 8.35 0.7911.34 14 0.79 8.53 0.77 10.37 15 0.83 8.15 0.77 10.41 16 0.83 8.30 0.7910.88 17 0.82 8.15 0.77 10.29 18 0.80 8.22 0.76 10.00 19 0.83 8.34 0.7510.38 20 0.84 8.41 0.78 11.02 21 0.81 8.24 0.79 10.55 22 0.82 8.31 0.7910.77 23 0.82 8.18 0.77 10.33 24 0.80 8.03 0.79 10.15 25 0.82 8.11 0.7910.51 26 0.82 8.35 0.77 10.54 27 0.83 8.41 0.76 10.61 28 0.78 8.49 0.7710.20 29 0.82 8.16 0.79 10.57 Comparative 0.72 8.05 0.69 7.99 Example 1

As apparent from the above, it can be seen that the dye-sensitized solarcell of the present invention exhibited an excellent photoelectricconversion efficiency.

Aspects of the present invention are as follows, for example.

<1> A photoelectric conversion element including:

a first electrode;

a hole blocking layer;

an electron transport layer;

a first hole transport layer; and

a second electrode,

wherein the first hole transport layer includes at least one of basiccompounds represented by general formula (1a) and general formula (1b)below:

where in the formula (1a) or (1b), R₁ and R₂ represent a substituted orunsubstituted alkyl group or aromatic hydrocarbon group and may beidentical or different, and R₁ and R₂ may bind with each other to form asubstituted or unsubstituted heterocyclic group containing a nitrogenatom.<2> The photoelectric conversion element according to <1>,wherein the electron transport layer includes an electron transportmaterial photosensitized with a photosensitizing material represented bygeneral formula (2) below:

where in the formula, R₃ represents a substituted or unsubstituted alkylgroup.<3> The photoelectric conversion element according to <2>,wherein the electron transport material is at least one selected fromthe group consisting of titanium oxide, zinc oxide, tin oxide, andniobium oxide.<4> The photoelectric conversion element according to any one of <1> to<3>,wherein the hole blocking layer includes titanium oxide.<5> The photoelectric conversion element according to any one of <1> to<4>,wherein the first hole transport layer includes an ionic liquid.<6> The photoelectric conversion element according to <5>,wherein the ionic liquid includes an imidazolium compound.<7> The photoelectric conversion element according to any one of <1> to<6>, further includinga second hole transport layer between the first hole transport layer andthe second electrode, the second hole transport layer including a holetransportable polymer material.<8> A solar cell includingthe photoelectric conversion element according to any one of <1> to <7>.

The “solar cell” according to <8> includes a first electrode, a holeblocking layer, an electron transport layer, a first hole transportlayer, and a second electrode, and uses at least one of basic materialsrepresented by the general formula (1a) and the general formula (1b) inthe first hole transport layer. This realizes a high internal resistanceand a high open circuit voltage, and makes it possible to obtain a solarcell having a favorable characteristic under room light.

DESCRIPTION OF THE REFERENCE NUMERAL

-   -   1 substrate    -   2 first electrode fixing device    -   3 hole blocking layer    -   4 electron transport layer    -   5 photosensitizing compound    -   6 hole transport layer    -   7 second electrode    -   8 lead line    -   9 lead line

The invention claimed is:
 1. A photoelectric conversion elementcomprising: a first electrode; an electron transport layer; a first holetransport layer; and a second electrode, wherein the first holetransport layer comprises a lithium compound and at least one of basiccompounds represented by formula (1a) and formula (1b):

where in the formula (1a) and (1b), R₁ and R₂ each independentlyrepresent a substituted or unsubstituted alkyl group or aromatichydrocarbon group and may be identical or different, and R₁ and R₂ maybind with each other to form a substituted or unsubstituted heterocyclicgroup that comprises a nitrogen atom, provided that the formula (1a) isnot


2. The photoelectric conversion element according to claim 1, whereinthe electron transport layer comprises an electron transport materialphotosensitized with a photosensitizing material represented by formula(2) below:

where in the formula (2), R₃ represents a substituted or unsubstitutedalkyl group.
 3. The photoelectric conversion element according to claim2, wherein the electron transport material comprises at least oneselected from the group consisting of titanium oxide, zinc oxide, tinoxide, and niobium oxide.
 4. The photoelectric conversion elementaccording to claim 1, further comprising: a hole blocking layer betweenthe first electrode and the electron transport layer, wherein the holeblocking layer comprises titanium oxide.
 5. The photoelectric conversionelement according to claim 1, wherein the ionic liquid in the first holetransport layer comprises an imidazolium compound.
 6. The photoelectricconversion element according to claim 1, further comprising: a secondhole transport layer between the first hole transport layer and thesecond electrode, wherein the second hole transport layer comprises ahole transportable polymer material.
 7. The photoelectric conversionelement according to claim 1, wherein the lithium compound is lithiumtrifluoromethane sulfonylimide or lithium diisopropylimide.
 8. Thephotoelectric conversion element according to claim 1, wherein the firsthole transport layer includes a spirobifluorene-based compound.
 9. Thephotoelectric conversion element according to claim 1, wherein the firsthole transport layer further comprises an ionic liquid.
 10. Thephotoelectric conversion element according to claim 1, wherein the firsthole transport layer comprises a basic compound represented by theformula (1b).
 11. The photoelectric conversion element according toclaim 1, wherein the first hole transport layer comprises a basiccompound represented by the formula (1a), and at least one of R₁ and R₂in the formula (1a) represents a substituted or unsubstituted aromatichydrocarbon group.
 12. The photoelectric conversion element according toclaim 1, wherein the first hole transport layer comprises a basiccompound represented by the formula (1a), and in the formula (1a), R₁and R₂ each independently represent an alkyl group substituted with anaromatic hydrocarbon group, or represent a substituted or unsubstitutedaromatic hydrocarbon group.
 13. The photoelectric conversion elementaccording to claim 1, wherein in the formula (1a) or (1b), at least oneof R₁ and R₂ represents a substituted or unsubstituted aromatichydrocarbon group.
 14. The photoelectric conversion element according toclaim 1, wherein in the formula (1a) or (1b), R₁ and R₂ eachindependently represent an alkyl group substituted with an aromatichydrocarbon group, or represent a substituted or unsubstituted aromatichydrocarbon group.
 15. A solar cell comprising the photoelectricconversion element according to claim 1.